Optical communication technology transferring data using optical carrier waves has been developed, and an optical waveguide has become widespread as a means for leading such optical carrier waves from one point to another point. This optical waveguide has a linear core section and a cladding section provided so as to cover the periphery thereof. The core section is constituted by a material that is substantially transparent to light of the optical carrier waves and the cladding section is constituted by a material having a lower refractive index than the core section.
In the optical waveguide, light which has been introduced from one end of the core section is carried to the other end while reflecting at the boundary with the cladding section. At the incidence side of the optical waveguide is arranged a light-emitting element such as a semiconductor laser and at the emission side is arranged a light-receiving element such as a photodiode. Light that has entered from the light-emitting element propagates through the optical waveguide and is received by the light-receiving element, and communication is carried out based on the flicker pattern of the received light or the strength pattern thereof.
Laying such optical waveguide on a substrate and constructing optical wiring has been examined. For example, in the electronic device disclosed in Patent Document 1, a plurality of optical waveguides is disposed on a substrate and, furthermore, an electrical wiring board on which a light-emitting element and a light-receiving element have been mounted is arranged at an end section of the optical waveguides.
However, such optical wiring is mostly mounted in an electronic device for the purpose of replacing a part of the electrical wiring. For this reason, when saving space of the entire wiring is considering, the optical wiring is surfically mounted with the electrical wiring on the main substrate like disclosed in Patent Document 1.
On the other hand, many electrical elements other than optical wiring and electrical wiring are mounted on this substrate. In recent years, the demand for the miniaturization of substrates is great, and the mounting density of electrical elements has also increased in association with this. However, since it is necessary for these electrical elements to be fixed to the substrate by solder or the like, it is difficult for the electrical elements and the optical elements to coexist in the same position in planar view. For this reason, there is the necessity of laying the optical waveguide so as to avoid electrical elements, as well as, when the number of optical elements is large, there is the necessity of laying by dividing into pluralities. As a result, the higher the mounting density of electrical elements becomes, the more many optical waveguides must be intricately disposed, and the number of production steps becomes very large and the total extension of the optical waveguide increases, thus leading to increase in transmission loss.